1. Field of the Invention
The present invention relates generally to a heat dissipating apparatus having a micro-structure layer and method of fabricating the same, and more particularly, to a heat dissipating apparatus having a micro-structure layer and method of fabricating the same employing a liquid-gas phase transition to dissipate heat.
2. Description of the Related Art
During the last decades, semiconductor fabrication techniques have both reduced the size and increased the functionality of electronic devices, but problems in terms of power consumption, heat dissipation, and reliability have inevitably derived from the process of integrating the electronic devices.
The main reason for the limited reliability of the above devices is that the electronic devices are driven by electricity power that is not fully utilized, and the unused portion of power is converted into heat energy, which dramatically raises the temperature of the whole system incorporating these devices. In the case that the operating temperature goes beyond the range permitted, erratic operation, system failure, and even damage may occur. For the new generation of high-density electronic products, the computation speed and operating frequency of the internal electronic devices thereof is much higher than conventional products. Thus, the amount of heat generated in the course of operation is significantly huge to easily result in their operating temperature exceeding the permitting range. Compounding the problem, along with the trend of miniaturized electronic devices, heat dissipating apparatus has shrunk the size as well to accommodate the desire for smaller products, which presents a big challenge to the fabricating technology in this field in terms of effective heat dissipation and product reliability.
To address the aforementioned problems, a passive cooling mechanism which adopts a liquid-gas phase transition in the fluid is employed in conventional technology. As illustrated in FIG. 5, with liquid-gas phase transition and capillary action in a heat pipe, the heat from a heat absorbing end (heat source) 50 is conducted via evaporation of the liquid to a heat dissipating end 51, and further with condensation of the vapor and capillary pull of the capillary structure, a circulated movement is provided for continually dissipating the heat generated by the electronic devices. Both Taiwanese Patent Publication of 528151 and 501722 disclose such heat dissipating apparatus incorporating the above heat pipe.
The heat dissipating efficiency of the above apparatus is determined by the capillary structure. If the dimensional precision and distribution of the capillary structures fail to comply with design requirements, the efficiency of the vaporized fluid moving from the heat-absorbing end to the heat-dissipating end may be degraded, and the efficiency of vaporized fluid returning to the heat dissipating end to be re-circulated after heat dissipation may also be degraded. While such heat dissipating apparatus is targeted for using on the miniaturized electronic devices, having the capillary structures dimensioned in micron (μm) scale adds more difficulty to precisely control the fabricating method.
U.S. Pat. No. 4,046,190 discloses a method of fabricating the capillary structure by means of sintered powdered metal. The method is to firstly spread a layer of highly heat conductive metal particles, such as copper, and then sinter under high temperature to form the desired capillary structure. However, a serious drawback associated with the fabrication method is found in the actual production, since the dimension of the capillary structure is not precisely controlled by such sintering method. For a capillary structure with dimensional precision required at the μm scale, the final sintered product usually does not meet the dimensional precision as required in the original design. Therefore, the heat dissipating efficiency is significantly degraded.
To solve the above problem, an injection molding process is adopted in the conventional technology, where injection molding process is performed using sintered copper powder. With characteristics of the injection molding process, the desired capillary structure or channel that fulfills the highly precise geometric dimension requirement is formed, so as to meet the precision requirement of the capillary structures. However, the process described above only solves the problem associated with forming the capillary structure. Other drawbacks remain to be solved, such as the density of the applied copper is relatively low compared to regular plated copper due to the high temperature used in injection molding resulting in a much lower thermal coefficient. Therefore, although heat can be dissipated by liquid-gas phase transition according to the process above, the efficiency of heat dissipation as a whole still awaits further improvement, and current needs for heat dissipating of electronic devices are not satisfied.
Consequently, it is desirable to develop a method for fabricating a heat dissipating apparatus having such a capillary structure layer that can increase the heat dissipation efficiency of the apparatus, wherein the fabricating method is simple and adaptable to rapid mass production.